1. Field of the Invention
The present invention relates to an actuator.
2. Description of the Related Art
A polymer actuator is more flexible than an actuator which is made from a conventional inorganic material, and has drawn attention because of having the feature of operating at a low electric power. Among the polymer actuators, a polymer actuator having a structure in which an ion-exchange resin is sandwiched between two electrodes is typical. This polymer actuator curves and deforms itself by making ions in an ion-exchange membrane migrate due to voltage applied between electrodes. Here, in order to stably retain the ions in the ion-exchange membrane, the actuator is usually covered with a layer (hereinafter sometimes abbreviated as a water-impermeable layer) of a material which suppresses the permeation of water.
For instance, Japanese Patent Application Laid-Open No. 2008-035682 discloses an actuator which suppresses the outflow of the ions from an ion-conductive polymer layer and the inflow of water by covering the surface of a structure including electrodes and the ion-conductive polymer layer (a cation-exchange resin layer) with the water-impermeable layer formed from a polymer. Furthermore, Japanese Patent Application Laid-Open No. 2008-035682 discloses an actuator which not only enhances the performance of suppressing the inflow of water and the like but also has the function of protecting the water-impermeable layer, by forming a metal layer on the surface of the water-impermeable layer.